Frequently, nerve injuries result in severe and lingering complications such as back pain, peripheral neuropathy, neck pain, carpal tunnel syndrome, and the like. One of these complications is persistent and debilitating nerve injury induced pain syndrome. Typically, this pain manifests itself through severe discomfort, peripheral numbness, a decreased range of bodily motion, and decreased muscular strength. Due to these symptoms, pain syndrome associated with nerve injury can disrupt one's ability to function adequately at work or even fulfill social obligations.
Present clinical treatment methods for pain syndrome associated with nerve injury are numerous and varied. Included among them: over-the-counter medications such as aspirin, acetaminophen, and other non-steroidal anti-inflammatory agents; prescription medications which include narcotics such as morphine and Demerol, steroids, and local injections of nerve blockers like lidocaine or xylocaine. Other interventions include the use of serotonin-specific reuptake inhibitors, which include fluoxetine, peroxitine and sertraline. Still other treatments include non-pharmacological interventions such as physical therapy, spine manipulation, therapeutic massage, and, in specially severe cases, even spinal cord surgery.
Unfortunately, the efficacy of these treatments is limited to certain symptoms for subgroups of patients. For some patients a given method may provide modest relief from pain, but the majority of patients continue to experience disabling pain in spite of these treatments. Given both the limited benefits of present clinical methodology and the number of individuals who suffer from pain associated with nerve injury, it is easy to see why nerve injury induced pain syndrome represent expensive and debilitating disorders that challenge the current health care system.
Some have experimented with the use of nalmefene and naloxone in treating spinal cord injuries. L & I. Faden et al., Opiate-Receptor Antagonist Nalmefene Improves Neurological Recovery after Traumatic Spinal Cord Injury in Rats through a Central Mechanism, 245 J. Pharmacology & Experimental Therapeutics, 742-48 (1988). For example, Faden and colleagues showed that the opiate-receptor antagonist nalmefene was 100 times more potent than naloxone in promoting the recovery of motor skills, such as walking ability, in rats following spinal cord injury. A large scale study in humans shows that naloxone did not statistically reduce tissue damage at or near the site of spinal cord injury. Michael Bracken et al., A Randomized, Controlled Trial of Methylprednisolone or Naloxone in the Treatment of Acute Spinal-Cord Injury, Vol. 322, New Eng. J. Med. (1990).
Naloxone is currently FDA approved for the treatment of respiratory depression secondary to opiate overdose. Naloxone is also used to diagnose opiate dependence. While naloxone blocks the high associated with opiates, its short half-life in vivo, typically between 30 and 81 minutes (Remington's Pharmaceutical Sciences, 17th Edition), severely limits its value by requiring multiple doses for effective treatment of opiate dependence. Opiate-receptor antagonists with greater half-lives, e.g., naltrexone which can be taken orally, are therefore more clinically attractive for the treatment of opiate dependence and have received FDA approval for this use.